a. Field of the Invention
This invention relates to a handwheel and a handwheel kit for enlarging a focussing ring of a rifle scope. In particular, the invention relates to a handwheel kit for fitting to a rifle scope focussing control to provide the rifle scope with a relatively large diameter handwheel for use as a focussing ring for adjusting the focus of the scope, as compared to a relatively small diameter focussing ring as originally provided on the rifle scope as manufactured. The invention further relates to a method of fitting such a relatively large handwheel to a rifle scope to provide an enlarged focussing ring.
b. Related Art
Many known designs of rifle scope (hereinafter referred to simply as a “scope”) include a focussing control comprising a relatively small diameter focussing ring furnished on a stub shaft projecting laterally from the barrel of the scope, the stub shaft being connected internally within the barrel to movable lens components for effecting adjustment of the scope focus. In this application, the term “relatively small” means a diameter less than the diameter of any part of the barrel of the scope. In optimum conditions, such a focussing ring may be sufficient to allow accurate focussing, but in more difficult conditions, such as in a cold climate, many users find the focussing ring too small to give the accurate focussing that the user requires.
In view of the above, it is known to exchange the focussing ring with a handwheel of a larger diameter by releasing the focussing ring from the scope and then fitting the larger diameter handwheel to the stub shaft projecting from the scope barrel. However, there is often a seal provided on the focussing ring to prevent the ingress of moisture into the scope barrel and if the focussing ring is removed, that seal may be lost. Moreover, there may be a friction arrangement between the focussing ring and the scope barrel, in order to give an appropriate “feel” to the focussing control. As such, the removal and discarding of the focussing ring is in general not recommended by scope manufacturers.
An alternative approach has been to provide a relatively large diameter handwheel having a hub with a central bore which is appropriately sized to fit over the outer surface of the scope focussing ring. The handwheel is then secured in position by means of three or more grub screws threaded into equally spaced radial bores provided through the hub wall, for engagement with the outer surface of the focussing ring. Typically, such grub screws have hexagonal sockets at one end to allow the turning thereof by means of an Allen key. Though in theory this solution would seem more appropriate, in that it does not disturb the arrangement of the focussing ring, in practice the engagement of the grub screws with the outer surface of the focussing ring may cause significant damage to that focussing ring if the handwheel is to be secured sufficiently firmly on tightening the grub screws. Moreover, the use of an Allen key to drive the grub screws can be very difficult in the confined region of the handwheel when fitted to the scope, and it is all too easy to lose one of the small grub screws.
It is a principal aim of the present invention to provide means whereby a relatively large handwheel may be fitted to a rifle scope without suffering the disadvantages discussed above of the known arrangements for achieving this.